Research On Simulation Of Advanced PWR Using RELAP5-HD Code

AP1000 is a Generation III+ reactor which is developed by Westinghouse based on proven technology building on decades of operating Westinghouse PWR experience. It's an innovative design which complies with all of the NRC regulatory and safety requirements,and also the advanced light water reactor utility requirements document (URD). The AP1000 is a two-loop reactor which has a net power of 1117MWe.Compared with the traditional PWR plants, AP1000 use passive safety systems which employ passive features, for example,compressed gas, gravity and natural circulation, rather than active equipments such as pumps and AC power, to drive the systems. This provides the great improvements in plant simplification, safety and reliability. The AP1000 passive core cooling system is comprised of the passive residual heat removal system (PRHR), the passive safety injection systems(PSIS)and the automatic depressurization system (ADS) which is significant to link up the three phase of PSIS effectively . The system structure, operating characteristics, and passive safety idea are much different from the current operating plants. To be familiar with the system structure of the advanced reactor, know well its operating characteristics, better understand its passive safety idea, and observe the typical multi-dimensional flow in the vessel,RELAP5-HD code is needed to simulate the AP1000 plant.RELAP5-3D is the latest version of the RELAP5 codes. The most important improvements that make RELAP5-3D different from the previous RELAP5 versions are the introduction of multi-dimensional hydrodynamics component and the multi-dimensional reactor kinetics model. Bywrapping RELAP-3D into the base architecture of GSE's premiere real-time simulator executive, SimExec, RELAP5-HD provides thermo-hydraulic solutions to plant operations in real-time without jeopardizing the integrity of INL's best estimate code.First, the AP1000 plant model is developed using the RELAP5-HD code. The model mainly includes the reactor vessel, steam generator, main loop, pressurizer, passive core cooling systems and control systems. Especially, the downcomer and core in the reactor vessel is modeled with multi-dimensional hydrodynamic component to represent the multi-dimensional flow. Then the model is validated through a null transient run, and the final results are compared with the AP1000 rated values. Besides, the flow mixing in the downcomer and core are analyzed. Next,a cold leg 10-in break is used as a transient to test the passive core cooling systems and the control system. After that, the validated model is used to study the typical accident in the PWR plant,such as main-feedwater-loss accident and main-steam-line-break accident. The response of AP1000 passive core cooling systems to the non-LOCA accident is studied. Besides, the multi-dimensional flow and asymmetry in the reactor vessel during the main-steam-line-break accident are analyzed. The results show that during the transient, passive core cooling system can be introduced automatically to remove the residual heat from the core and assure the safety of the reactor. During the main-steam-line-break accident, the asymmetry in the loop and passive system response will lead to the asymmetry in the reactor vessel.